Thursday, October 28, 2010

Tiny African Tadpole a Big Sucker to Its Prey

Scientists have discovered that the tiny tadpoles of a species of African frog have an unusual feeding method: They suck in their prey, just as fish do.

Suction feeding, which biologists from the University of California at Berkeley observed during high-speed video filming of African dwarf clawed frog (Hymenochirus boettgeri) tadpoles, is extremely rare among frogs.

Most tadpoles are suspension feeders, filtering out tiny particles while continuously pumping water. As adults, most aquatic frogs use their hands to scoop up their prey or capture it in their large mouths.

Tadpoles of the African dwarf clawed frog (Hymenochirus boettgeri), however, visually track their prey, chase it, and then suck it down through an extendable tube-like mouth, said Stephen Deban, co-author of a report on the discovery published in the November 7 issue of the journal Nature. Deban is now a postdoctoral researcher the University of Utah in Salt Lake City.

He likens the Africa frog's behavior to a human sucking down soda with a straw.

"The tadpole basically lowers the floor of its mouth very quickly, while raising the head and extending the mouth tube," he said. "These movements increase the space inside the mouth and water flows inward as a result."

Once the prey is inside the tadpole's mouth, the water is slowly squeezed out through gill slits at the rear of the mouth cavity.

Wendy Olson, a co-author of the study who is currently a postdoctoral researcher at Dalhousie University in Canada, said that when she and Deban show the tadpole-feeding video to other scientists, "most of them assume right away that they are looking at a fish."

The African dwarf clawed frog is native to rain forests of central and western Africa and is a common pet in household aquariums.

Suction Advantage

Tadpoles of the African dwarf clawed frog start feeding when their bodies are less than 0.04 inches (one millimeter) long, making them one of the smallest free-swimming vertebrates in the world when they start eating.

The tadpoles grow continuously and their bodies reach about 0.4 inches (one centimeter) before they transform into frogs.